1. Field of the Invention
The present invention relates to a test method of a structure body included in a micromachine which is manufactured by surface micromachining, and a micromachine and a structure body which are manufactured by employing the test method.
2. Description of the Related Art
A micromachine is also called a MEMS (Micro Electro Mechanical System) or a MST (Micro System Technology), and refers to a general system in which a minute mechanical structure body (also referred to as a microstructure body, or simply, a structure body) and an electric circuit are combined. In addition, a micromachine includes a bulk micromachine in which a structure body is manufactured by utilizing crystal anisotropy of a silicon substrate and a surface micromachine in which a spatial structure body is manufactured by stacking thin films over various substrates. When manufacturing either micromachine, a structure body having a certain function and a peripheral circuit (electric circuit) are integrated in an on-chip mode or an on-package mode. Here, in an on-chip mode, an electric circuit having a semiconductor element and a structure body are manufactured over the same substrate, whereas, in an on-package mode, an electric circuit and a structure body each manufactured over a different substrate are put in one package to be a final product.
A cause to decrease yield is different between a structure body manufactured by a surface micromachining or bulk micromachining technique and a peripheral circuit manufactured by a conventional LSI technique. Therefore, yield of a micromachine having both the structure body and the peripheral circuit is the product of the yield of the structure body and the yield of the electric circuit either in an on-chip mode or an on-package mode; therefore, it is difficult to increase productivity.
In particular, yield is low in a structure body. There are various reasons such as a problem that a substrate to which a process check, like a check on a film thickness or an etching rate, is carried out cannot be returned to a process and is required to be thrown away, it is difficult to evaluate whether a structure body operates normally until the structure body is mounted on a final product, and the like. In order to solve these problems, various researches are carried out (see, for example, Patent Document 1: Japanese Published Patent Application No. 2005-43514 and Patent Document 2: Japanese Patent No. 3549105).
In Patent Document 1, there is proposed a measuring method and a test method of a device, which precisely determine whether a structure body is transformed due to inner stress or whether a characteristic that is set at a time of designing is obtained. In addition, in Patent Document 2, there is proposed a method in which a mechanical characteristic of an actuator is tested by utilizing a frequency characteristic of a structure body.
By the techniques as described above, a structure body can be tested by microscope observation, an electric characteristic measurement, or the like, and a substrate is not required to be thrown away after the test. However, for example, the test in Patent Document 1 is carried out to a test pattern, and thus, a manufactured structure body itself cannot be tested. In addition, the test in Patent Document 2 can be carried out only after completing manufacturing of a structure body, and thus, a test for confirming a process cannot be carried out.
In general, it is not easy to implement a test of process confirmation or an electric characteristic to all the structure bodies that are manufactured over the substrate since, because of complicated structures and mechanisms, a high technique and an expensive device are necessary and the test takes long time. In addition, an electric characteristic measurement is carried out by making a needle of a prober be in contact with a substrate, whereby a risk of breaking a structure body with a three-dimensional spatial structure is increased, differently from a general semiconductor element.
In addition, when a test is carried out by making a needle of a prober be in contact, a layer in a portion where the needle is in contact is peeled, or a substrate is contaminated due to a dust which has fallen.
When a contact test method is used in a manufacturing process of a general semiconductor element, a substrate is always cleaned and returned to the process. However, in the case of a micromachine with a three-dimensional spatial structure having a space, a substrate cannot be cleaned since a structure body is broken.
Further, a space in a structure body is formed by removing a sacrifice layer below a structure layer by etching. Here, when the structure layer is formed by using an opaque material (in many cases, the structure layer is opaque since metal is used for the structure layer), it is impossible to test whether the sacrifice layer is completely removed by sacrifice layer-etching, using a simple means such as an optical microscope. When a test is carried out, a substrate is divided after sacrifice layer-etching, and a cross-section thereof is observed by a SEM or the like. However, even when it is found, by this test, whether the sacrifice layer is completely removed, the substrate which has been already divided cannot be returned to the process.
Accordingly, although a peripheral circuit which operates assuredly is selected by a test when a structure body and the peripheral circuit are integrated in an on-package mode, it is difficult to test all the structure bodies, and all the structure bodies are tested for the first time in a final test for testing whether the structure body operates normally after packaging. This is a cause to significantly decrease productivity of a micromachine.